The present disclosure relates generally to a method for inspecting the ring gear in a gearbox, and particularly to a method for inspecting a ring gear in a gearbox for the detection, characterization and/or sizing of defects therein.
Recently, wind turbines have received increased attention as environmentally safe and relatively inexpensive alternative energy sources. With this growing interest, considerable efforts have been made to develop wind turbines that are reliable and efficient.
Generally, a wind turbine includes a rotor having multiple blades. The rotor is mounted to a housing or nacelle, which is positioned on top of a truss or tubular tower. Utility grade wind turbines (i.e., wind turbines designed to provide electrical power to a utility grid) can have large rotors (e.g., 30 or more meters in diameter). Blades on these rotors transform wind energy into a rotational torque or force that drives one or more generators that may be rotationally coupled to the rotor through a gearbox. The gearbox steps up the inherently low rotational speed of the turbine rotor for the generator to efficiently convert mechanical energy to electrical energy, which is typically fed into a utility grid.
Wind turbine gearboxes are subject to a large amount of loads. Most of these loads are from the rotor and can include main shaft torque, weight of the rotor, axial thrust forces and other dynamic loads. Some of these loads will be steady, some may be transient, while others may vary randomly or periodically. All of the loads contribute to fatigue damage and wear on the various components of the gearbox. Because the gearbox is difficult to remove and replace, failure of any gearbox component can result in a lengthy and expensive repair process. For example, to remove a gearbox from an existing wind turbine, a large crane must be transported to and erected on site. The wind turbine will be off-line and out of energy production during the repair process.
One component of a gearbox that can fail is the ring gear. One known inspection method for the ring gear is a visual inspection using borescope-type equipment. Visual testing can be used to find large defects such as missing sections of the gear teeth but the capability of the inspection for finding small crack-like defects is not as high as possible. Improving the capability of the visual inspection would result in a time-consuming evaluation resulting in increased downtime and expense. Any inspection method which uses the borescope holes in the gearcase for access will have limited capability for finding small crack-like defects. For instance, any visual surface inspection method would need to interrogate each gear tooth surface. This process would be very difficult, if possible, due to the limited amount of access ports.